Device for introducing light into a waveguide, device for emitting light from a waveguide and method for manufacturing such devices

ABSTRACT

The invention relates to a device for introducing light into a waveguide, which device comprises: a light source, preferably an electro-optical converter, more preferably a VCSEL, for generating a light beam; a reflector for receiving at least a part of the light beam and for reflecting at least a part of the received part, wherein the waveguide and the material layer lie substantially mutually in line and both rest at least partially on a substantially flat substrate, wherein the light source and the reflector are positioned relative to the waveguide such that at least a part of the reflected part is introduced into the waveguide. The invention also relates to a device for emitting light from a waveguide. The invention further relates to a method for manufacturing such devices.

Device for introducing light into a waveguide, device for emitting lightfrom a waveguide and method for manufacturing such devices

The invention relates to a device for introducing light into awaveguide, which device comprises: a light source, preferably anelectro-optical converter, more preferably a VCSEL, for generating alight beam; a reflector for receiving at least a part of the light beamand for reflecting at least a part of the received part, which reflectorcomprises an at least partially concave reflecting surface and at leasta part of an end surface of a material layer, and a waveguide providedwith a light-conducting layer wherein the waveguide and the materiallayer lie substantially mutually in line and both rest at leastpartially on a substantially flat substrate, wherein the light sourceand the reflector are positioned relative to the waveguide such that atleast a part of the reflected part is introduced into the waveguide. Theinvention also relates to a device for emitting light from a waveguide,which device comprises: a light receiver, preferably an opto-electricalconverter, more preferably a photodiode; a waveguide provided with alight-conducting layer, wherein the waveguide and the reflector arepositioned relative to the light receiver such that at least a part ofthe reflected part is received by the light receiver, and a reflectorfor receiving at least a part of a light beam emitted from the waveguideand for reflecting at least a part of the received part, which reflectorcomprises an at least partially concave reflecting surface and at leasta part of an end surface of a material layer, wherein the waveguide andthe material layer lie substantially mutually in line and both rest atleast partially on a substantially flat substrate. The invention furtherrelates to a method for manufacturing such devices.

American patent specification U.S. Pat. No. 6,108,472 describes a devicefor emitting light from a waveguide resting on a substrate. Both thewaveguide and a reflective surface are herein formed from one and thesame silicon layer which rests on an insulator layer arranged on asubstrate in a SOI (silicon-on-insulator) configuration. Via thereflective layer the light can be redirected to a light receiver. Theadvantage of the known device is that the mutual positioning of thewaveguide and the reflective surface can be defined by means of a singlelithographic processing step. As well as advantages, the known devicealso has drawbacks. An important drawback of the known device is thatthe generally (slightly) diverging light incident upon the reflectivesurface forming part of the (monocrystalline) silicon part is divergedconsiderably (further) during reflection of the light in the directionof the reflecting surface. It will thus be possible to detect only arelatively small part of the reflected light with the light receiver.

U.S. Pat. No. 5,416,861 (D1) discloses an optical synchronous clockdistribution device, wherein light beams emitted by a waveguidecontained in a dielectric layer can be reflected via a concavemicro-mirror towards a light detector. The concave micro-mirrorconverges the commonly diverging light beam resulting in an improveddetection of emitted light. Besides this advantage, the known device hasseveral drawbacks. The device known from D1 makes part of the field ofmicro(structural)-technology, thereby comprising severalmicro-dimensioned components, such as said micro-mirror. The objectiveproblem underlying D1 is that it will be very difficult and hard toaccurately place the micro-mirror into the optimal position between twoneighbouring dielectric (micro-)layers for reflecting the emitted lightbeams as a whole.

The present invention has for its object to provide an improved devicefor introducing * respectively emitting light into respectively from awaveguide, whereby light can be redirected in relatively efficientmanner.

The invention provides for this purpose a device for introducing lightinto a waveguide of the type stated in the preamble, characterized inthat the waveguide and the material layer are formed at least partiallyby the same layer structure. Both the reflector and the waveguide cantherefore be manufactured from one and the same material layer, whichcan both be deposited in one process run. This is advantageous since apost-positioning of the reflector onto the substrate is no longerneeded. The layer is deposited onto the substrate in one process run,and subsequently the reflective will be etched in the material layer.This leads to a more simple a efficient device for introducing lightinto a waveguide. The main direction of the reflected part herein liessubstantially perpendicular to the main direction of the received part.Due to the concave form of the reflector the light will be convergedslightly during reflection of the light by the reflector, whichgenerally results in a relatively intensive reflected light beam whichcan further be received by the waveguide. Because of the convergingaction of the reflected light beam, it will be possible for thewaveguide to receive all of, or at least a relatively large part of thelight beam. In relatively simple manner a device according to theinvention is thus obtained with which a light beam can be redirectedwith a relatively high efficiency.

It is noted that within the scope of the present invention, the term‘light’ comprises all electromagnetic phenomena and does not thereforepreclude frequencies outside the visible spectrum.

EP 0816878 describes a method and device for introducing light into awaveguide, wherein a recess is arranged in a substrate, whereafter ametal layer, which serves as mirror, is arranged on a side face of thisrecess. The recess is then filled with a waveguide material, so that awaveguide is formed. As light source can be used a VCSEL (verticalcavity surface emitting laser) which is mounted on the whole ofsubstrate and reflecting side surface and waveguide arranged thereinsuch that the light emitted by the light source or VCSEL is introducedinto the waveguide via the reflecting surface. Forming of the recess andarranging waveguide material therein is however difficult. The number ofsuitable materials is furthermore small and the possibilities of makingmore complex networks of waveguides are limited. Another relevantdrawback of this already known device is that a flat mirror is alsoused, whereby an incident (slightly) diverging light beam will bediverged further during reflection via the mirror, whereby part of thelight beam will already exit the waveguide just after reflection, whichis generally undesirable.

The material layer can be built up from a plurality of (sub)layers. Thewaveguide can comprise a light-conducting channel, limited in width, ora light-conducting ‘slab’, in principle extending without limit in thewidth. Since they rest on the same substrate and lie at the same height,the reflector or reflecting face and the waveguide are in principle wellaligned relative to each other, whereby the part of the reflected partintroduced into the waveguide will in principle be large.

The light source preferably comprises a VCSEL. A VCSEL is small andcompact, readily available, can be arranged relatively simply and isfound to be very satisfactory in practice. A LED or a laser diode canfor instance also serve as light source, as can a passive element suchas a glass fibre or a reflector. The light-conducting layer can hereinbe built up at least partially from at least one of the materials:silicon oxynitride; silicon nitride, for instance in stoechiometric orsilicon-rich configuration; silica, for instance Ge- or F-doped; apolymer, for instance polyimide, polyurethane or BCP; an epoxy, forinstance SU8; indium phosphide, gallium arsenide; lithium niobate.Structures built up from such materials are common and much used aswaveguides, although other waveguide materials are also suitable.

In preference the end surface of the material layer is at least partlyprovided with a first part of a metal layer. The metal layer gives thereflecting surface a larger reflection coefficient, so that thereflected part of the part received by the reflector will be larger,which will increase the total efficiency. A second part of the metallayer can herein form an electrode for the light source. The metal layercan then also serve as electrical connection, for instance of the VCSELor the photodiode.

The invention also provides a device for emitting light from a waveguideof the type stated in the preamble, characterized in that the waveguideand the material layer are formed at least partially by the same layerstructure. Both the reflector and the waveguide can therefore bemanufactured from one and the same material layer, which can both bedeposited in one process run. This is advantageous since apost-positioning of the reflector onto the substrate is no longerneeded. The layer is deposited onto the substrate in one process run,and subsequently the reflective will be etched in the material layer.This leads to a more simple a efficient device for emitting light from awaveguide. The main direction of the reflected part herein liessubstantially perpendicular to the main direction of the received part.

The light receiver preferably comprises a photodiode. A photodiode issmall and compact, readily available, can be arranged relatively simplyon the substrate and is found to be very satisfactory in practice. A PINfor instance, or a passive element such as a glass fibre or a reflectorcan however also serve as light receiver.

In both devices the reflected part is bundled and oriented to a greateror lesser extent by the curvature as stated above, whereby the partintroduced into the waveguide, respectively the part received by thelight receiver is increased, which will cause the total efficiency toincrease. The reflecting surface can also comprise at least one facet.

‘Facet’ is here understood to mean a substantially flat part of asurface. The reflecting surface can for instance be an anisotropicallyetched etching surface at an angle to the main direction of thewaveguide, or be built up for instance from a number of facets in anangular curved form. The reflecting surface can also take an angularform and thus be provided with one or more angles, whereby a concave andtherefore converging action of the reflecting surface can also beachieved. The profile of the reflecting surface can be chosen subject tothe type and the form of the light conductor and light source or lightreceiver.

The substrate herein preferably consists substantially of silicon.Silicon is much used as basic material for integrated and miniaturizeddevices. At least part of the required layers and structures can then bearranged in and/or on the substrate by means of thin-film techniques;etching techniques and photolithographic techniques known from the fieldof ‘microsystem technology’, also referred to as ‘microstructuraltechnology’.

The invention further provides methods for manufacturing devices of thetypes stated in the preamble, comprising the steps of: A) depositingarranging on a substrate a waveguide (2, 2′) and a reflector (5, 5′)formed by an end surface (11, 11′) of a material layer (12, 12′) onto asubstrate, wherein the waveguide is provided with a light- conductinglayer (17, 17′), B) applying a concave reflector (5, 5′) byposition-selective etching an end surface (11, 11′) of said materiallayer (12, 12′), and , and C) positioning a light source respectivelylight receiver such that light displacement between the waveguide on theone hand and the light source respectively light receiver on the otheris possible via the reflector. Advantageously, step A) can be carriedout in one process run, wherein both the waveguide and the materiallayer can have the same layer structure.

The light-conducting layer can herein be built up at least partly fromat least one of the materials: silicon oxynitride; silicon nitride, forinstance in stoechiometric or silicon-rich configuration; silica, forinstance Ge- or F-doped; a polymer, for instance polyimide, polyurethaneor BCP; an epoxy, for instance SU8; indium phosphide, gallium arsenide;lithium niobate, although other waveguide materials are also suitable.This choice of materials is in principle unlimited. The material layerand the waveguide are herein preferably structured at least partly thesame in terms of layer structure and materials. This entails asignificant simplification of the production process since the number oflayers and processing steps required can hereby be limited considerably.

The method herein preferably comprises the step: X.;XX., of forming atleast a part of the end surface by means of position-selective etchingof the material layer. Position-selective etching is a common andwell-developed technology with which it is possible to realize withgreat precision a well-defined end surface or reflecting surface. Theposition-selective etching can herein substantially comprise isotropicetching. In isotropic etching, i.e. not varying in direction, the formedend surface or reflecting surface will be curved, whereby the reflectedpart is bundled and oriented to a greater or lesser extent which willincrease the total efficiency. Position-selective etching can alsocomprise substantially anisotropic etching. It is thereby possible torealize an etching surface or reflecting surface with one or morefacets.

The methods herein preferably also comprise the step: Y.;YY., ofarranging a metal layer on at least apart of the end surface of thematerial layer. Arranging a metal film and patterning thereof is a usualand well-developed technology with which it is possible to realize awell-defined metal pattern relatively simply and with great precision.

The method can herein also comprise the step: Z.;ZZ., of arranging alight-conducting medium such as a gel, glue or polymer with a suitablerefractive index in order to improve the optical coupling between thelight source or the light receiver and the waveguide. The totalefficiency of the optical coupling can thus be increased.

The invention is elucidated hereinbelow with reference to three devicesaccording to the prior art and two non-limitative embodiments of devicesaccording to the invention.

For this purpose:

FIG. 1 shows a schematic cross-section of a first known device foroptical coupling of a glass fibre to a waveguide;

FIG. 2 shows a schematic cross-section of a second known device foroptical coupling of a glass fibre to a waveguide;

FIG. 3 shows a schematic cross-section of a third known device foroptical coupling of an active light source to a waveguide;

FIG. 4 shows a schematic cross-section of a first preferred embodimentof a device for introducing light into a waveguide according to theinvention, and

FIG. 5 shows a schematic cross-section of a second preferred embodimentof a device for emitting light from a waveguide according to theinvention.

FIG. 1 shows a first known device 101 for optical coupling of awaveguide 102 to a glass fibre 121. At least a part 109 of a light beam122 fed by glass fibre 121 is introduced into waveguide 102. Glass fibre121 rests in a V-shaped groove 123 which is etched out in a substrate108, usually a silicon wafer. For a better optical coupling a gel orglue 124 is usually applied between glass fibre 121 and waveguide 102.Since the glass fibre 121 is generally much thicker than waveguide 102,glass fibre 121 lies partly recessed into V-shaped groove 123. This isnecessary for a good mutual alignment of light-conducting glass fibrecore 125 and a light-conducting layer 117 forming part of waveguide 102.This first known device 101 is relatively complex and the number ofsteps for manufacture thereof is relatively large, the etching out ofthe V-shaped groove 123 being particularly difficult and time-consuming.

FIG. 2 shows a second known device 201 for optical coupling of awaveguide 202 to a glass fibre 221. At least a part 209 of a light beam222 fed by glass fibre 221 is introduced into waveguide 202. Waveguide202 with substrate 208 is sawn through and glass fibre 221 is fixed withan outer end 225 against the sawn surface 226. This second known device201 is also relatively complex and the number of steps for themanufacture thereof is relatively large, the arranging and positioningof outer end 225 of glass fibre 221 against the saw cut 226 beingparticularly difficult and time-consuming.

FIG. 3 shows a third known device 301 for optical coupling of awaveguide 302 to an active light source 303, for instance a VCSEL 313.Waveguide 302 with substrate 308 is again sawn through and opticalelement 303 is fixed against the sawn surface 326. This third knowndevice 301 is also relatively complex and the number of steps formanufacture thereof is relatively large, the arranging and positioningof active light source 103 against saw cut 326 being particularlydifficult and time-consuming.

FIG. 4 shows a first preferred embodiment 1 of a device for introducinglight into a waveguide according to the invention, wherein a light beam4 is generated by a VCSEL 13. A part 6 of the light beam 4 is receivedby a reflecting surface 10. A part 7 of the received part 6 isreflected, a part 9 of this reflected part 7 being introduced intowaveguide 2 or a light-conducting layer 17 forming part of waveguide 2.Waveguide 2 is built up from a number of layers 17,2 a,2 b arranged on asubstrate 8, in this case a silicon wafer. Light source 3 is arranged inflip-chip mounting on substrate 8 with layer structure 12,12 a,12 b;14,15,16; 2,2 a,2 b,17. The reflecting surface 10 is manufactured bymeans of position-selective isotropic etching of a material layer 12arranged on 10 substrate 8. A curved end surface 11 is thus created onwhich is arranged a first part 14 of a metal layer 15. Material layer 12is build up from two (sub)layers 12 a, 12 b which can be deposited inone process run with the layers 17,2 a,2 b from which waveguide 2 isconstructed.

Advantages of this first preferred embodiment 1 are:

-   -   the material layer (12) can be arranged at least partly        simultaneously with the waveguide (2), which means a significant        simplification of the production process since the required        number of layers and processing steps can hereby be limited        considerably;    -   the entire layer structure 12,12 a,12 b; 14,15,16; 2,2 a,2 b,17        can be applied by means of thin-film techniques, etching        techniques and photolithographic techniques known from the field        of ‘microsystem technology’, also referred to as        ‘microstructural technology’;    -   the reflector 5 or reflecting surface 10 and the waveguide 2        rest on the same substrate 8 and therefore lie in principle at        the same height, whereby they are in principle properly aligned        relative to each other, and the part 9 introduced into waveguide        2 will in principle be large;    -   the device 1 is compact;    -   the VCSEL 13 is small and compact, readily obtainable, can be        arranged relatively simply and is found to be very satisfactory        in practice;    -   due to the curve of the reflecting surface 10, the reflected        part 7 is bundled and oriented to a greater or lesser extent,        whereby the part 9 introduced into waveguide 2 will be        increased;    -   the metal layer 15 gives the reflecting surface 10 a large        reflection coefficient, so that the reflected part 7 of the        incident part 6 will be large;    -   a second part 16 of metal layer 15 can also serve as electrical        connection for the VCSEL 13;    -   by coupling the light source 3 or VCSEL 13 more or less directly        to waveguide 2, an intermediary glass fibre 121, 221 is no        longer required.

FIG. 5 shows a second preferred embodiment 1′ of a device for emittinglight from a waveguide according to the invention, wherein a light beam9′ emitted from a waveguide 2′ is received and reflected by a reflector5′, whereafter a part 4′ of the reflected part 6′ is received by a lightreceiver 3′, for instance a photodiode 13′. The advantages of thissecond embodiment 1′ are mutatis mutandis the same as the statedadvantages of the first preferred embodiment 1.

It will be apparent for a person skilled in the relevant field that theinvention is not limited to the described and shown embodiments, andthat a number of further variations is possible within the scope of theinvention.

1-26. (canceled)
 27. A device comprising: (a) a light source forgenerating a light beam; (b) a reflector for receiving at least a partof said light beam and for reflecting at least a part of the receivedpart, wherein said reflector comprises: (i) a reflecting surface that isat least partially concave, and (ii) at least a part of an end surfaceof a material layer; and (c) a waveguide provided with alight-conducting layer, wherein said waveguide and said material layerlie substantially mutually in line and both rest at least partially on asubstantially flat substrate, wherein said light source and saidreflector are positioned relative to said waveguide such that at least apart of the reflected part is introduced into the waveguide; whereinsaid waveguide and said material layer are formed at least partially bythe same layer structure.
 28. The device of claim 27, wherein saidlight-conducting layer is built up at least partially from at least oneof the materials silicon oxynitride, silicon nitride, silica, a polymer,an epoxy, indium phosphide, gallium arsenide, and lithium niobate. 29.The device of claim 27, wherein in terms of structure (layer structureand materials), said material layer is at least partially the same assaid waveguide.
 30. The device of claim 27, wherein the main directionof the reflected part lies substantially perpendicular to the maindirection of the received part.
 31. The device of claim 27, wherein saidend surface of said material layer is at least partly provided with afirst part of a metal layer.
 32. The device of claim 31, wherein asecond part of said metal layer forms an electrode for said lightsource.
 33. The device of claim 27, wherein said reflecting surfacetakes an at least partially angular form.
 34. The device of claim 27,wherein said reflecting surface comprises at least one facet.
 35. Thedevice of claim 27, wherein said substrate consists substantially ofsilicon.
 36. A device comprising: (a) a light receiver; (b) a waveguideprovided with a light-conducting layer, wherein said waveguide and areflector are positioned relative to said light receiver such that atleast a part of the reflected part is received by said light receiver,and (c) said reflector for receiving at least a part of a light beamemitted from said waveguide and for reflecting at least a part of thereceived part, wherein said reflector comprises: (i) a reflectingsurface that is at least partially concave, and (ii) at least a part ofan end surface of a material layer; wherein said waveguide and saidmaterial layer lie substantially mutually in line and both rest at leastpartially on a substantially flat substrate; and wherein said waveguideand said material layer are formed at least partially by the same layerstructure.
 37. The device of claim 36, wherein said light-conductinglayer is built up at least partially from at least one of the materialssilicon oxynitride, silicon nitride, silica, a polymer, an epoxy, indiumphosphide, gallium arsenide, and lithium niobate.
 38. The device ofclaim 36, wherein in terms of structure (layer structure and materials),said material layer is at least partially the same as said waveguide.39. The device of claim 36, wherein the main direction of the reflectedpart lies substantially perpendicular to the main direction of thereceived part.
 40. The device of claim 36, wherein said end surface ofsaid material layer is at least partly provided with a first part of ametal layer.
 41. The device of claim 40, wherein a second part of saidmetal layer forms an electrode for said light receiver.
 42. The deviceof claim 36, wherein said reflecting surface is at least partiallyangular.
 43. The device of claim 36, wherein said reflecting surfacecomprises at least one facet.
 44. The device of claim 36, wherein saidsubstrate consists substantially of silicon.
 45. A method comprising:(a) depositing a waveguide and a material layer onto a substrate,wherein said waveguide is provided with a light-conducting layer; (b)applying a concave reflector by position-selective etching an endsurface of said material layer; and (c) positioning one of a lightsource and a light receiver such that light displacement is possible viasaid reflector between (i) said waveguide and (ii) said one of saidlight source and said light receiver.
 46. The method of claim 45,wherein said light-conducting layer is built up at least partially fromat least one of the materials silicon oxynitride, silicon nitride,silica, a polymer, an epoxy, indium phosphide, gallium arsenide, andlithium niobate.
 47. The method of claim 45, wherein in terms of layerstructure and materials said material layer and said waveguide have atleast partially the same structure.
 48. The method of claim 45, furthercomprising (d) forming at least a part of said end surface by means ofposition-selective etching of said material layer.
 49. The method ofclaim 48, wherein said position-selective etching comprises isotropicetching.
 50. The method of claim 48, wherein said position-selectiveetching comprises anisotropic etching.
 51. The method of claim 45,further comprising (d) arranging a metal layer on at least a part ofsaid end surface of said material layer.
 52. The method of claim 45,further comprising (d) arranging a light-conducting medium with asuitable refractive index in order to improve the optical couplingbetween (i) said one of said light source and said light receiver, and(ii) said waveguide.